This invention relates to a power plant using a reformer to supply hydrogen to a fuel cell, and in particular, to a power plant using an electrochemical autothermal reformer (EATR) to provide hydrogen fuel to the fuel cell.
A fuel cell is an electrochemical cell that converts the chemical energy of a fuel directly into electric energy in a continuous process. The overall fuel cell reaction typically involves the combination of hydrogen with oxygen to form water. For example, at 25.degree. C. and 1 atm pressure, the reaction H.sub.2 -1/2(O.sub.2).fwdarw.H.sub.2 O takes place with a free energy change (.DELTA.G) of -56.69 kcal/mole. In a galvanic cell, this reaction produces a theoretical cell voltage of 1.23 volts. Actual values are typically within the range of 0.9 to 1.1 volts. The main types of fuel cells used today include proton exchange membrane fuel cells, phosphoric acid fuel cells, alkaline fuel cells, solid oxide fuel cells, and molten carbonate fuel cells. Details on these individual technologies is found in "Fuel Cells, A Handbook (Revision 3)" published January, 1994 by the U.S. Department of Energy Office of Fossil Energy, incorporated herein by reference.
Fuel cells are limited by their need for pure hydrogen fuel. Most types of fuel cells are sensitive to even small amounts of impurities. A "reformer" is a known device in which a hydrocarbon fuel is mixed with steam, in the presence of a catalyst, to convert the fuel/steam mixture to hydrogen, carbon monoxide, carbon dioxide, water, and impurities. Since most known reformers are sensitive to the presence of impurities, impurities such as sulfur are generally removed from the fuel before entering the reformer. Most reformers leave small amounts of carbon monoxide (CO), typically about one mole percent, in the reformat or reformer product gas. Additional mechanisms are required to almost completely eliminate CO and other potentially harmful impurities from the reformer product gas. Such additional mechanisms add to the manufacturing and processing costs of electricity generating systems using fuel cells.